Need VFS hooks for directories/files
libdvdread has support for hooking the stream API so that virtual filesystems can be supported: https://code.videolan.org/videolan/libdvdread/blob/master/src/dvdread/dvd_reader.h#L74
Sadly that is reserved for opening ISO images or discs, since there are no hooks for readdir, open, close, etc. that would be needed for reading DVDs from VFS directories - libdvdread is hardcoded to only use standard libc functions there.
In Kodi, we currently load libdvdread with dlopen() and monkey-patch libc stdio. We'd really really rather not do that any more :-)
@jbk This is about the stuff I briefly asked you at the FOSDEM dinner last week. You wanted to know "well then how do we play DVDs from samba shares in VLC?" - turns out you kind of don't
dvd:// MRLs. It falls back to the mpegps demuxer, so menus etc. etc. don't work. This is true for both ISOs and VIDEO_TS directories.